During the production of electronic devices, there is sometimes a need to mount an integrated circuit die or chip onto a carrier. After mounting, electrical connections are made between the chip and the carrier before the product is molded into a semiconductor package, typically by the use of bonding wires. These bonding wires may be attached to bond pads on the chip and the carrier respectively by ultrasonic welding using an ultrasonic transducer.
The ultrasonic transducer is integrated into a wire-bonding machine. Since very fine wires and bond pitches are involved, the manner in which the ultrasonic transducer is mounted to the wire-bonding machine is very important. For example, if the ultrasonic transducer is mounted such that vibrations from the transducer are transferred to a mounting bracket, ultrasonic energy loss can result. If there is excessive vibration, the transducer characteristics, such as its frequency spectrum characteristics, may be changed, thereby affecting the stability of the transducer. Furthermore, the impedance of the transducer may change unpredictably, making it harder to control. Therefore, it is important to mount the ultrasonic transducer such that vibration generated during ultrasonic bonding is isolated to the transducer itself, and as far as possible, these vibrations are not transmitted to the rest of the wire-bonding machine.
In the case of a flange-mounted ultrasonic transducer, one way in which vibration to the wire-bonding machine can be minimized is disclosed in U.S. Pat. No. 6,135,339 for “Ultrasonic Transducer with a Flange for Mounting on an Ultrasonic Welding Device, in particular on a Wire Bonder”. This patent teaches locating the flange on a nodal point of the longitudinal vibration of the horn, and also forming the flange with a sufficient length such as to introduce a nodal point for radial vibration of the horn so as to locate a mounting point at the said radial nodal point. The ultrasonic transducer is mounted at the positions of these radial nodal points so that vibrations at the mounting positions are the lowest possible, and thereby reducing the transmission of vibration to the wire-bonding machine to which the transducer is mounted.
The problem with this approach is that the length of the flange may be lengthened in order to establish the said radial nodal point, as recognized in the patent disclosure itself. This modification is not desirable as more space is consequently required in the wire-bonding machine to locate the ultrasonic transducer, whereas it would be more desirable to make the components of the wire-bonding machine as compact as possible. Furthermore, using this approach still serves to impart significant vibration to the mounting because although the flange is located at a radial nodal point, the material of the flange is considerably larger than the nodal point itself. As a result, the effectiveness of the method is reduced.